The present invention pertains to the field of cartridge library systems for the automated storage and retrieval of data cartridges. More specifically, the cartridge library system includes at least one array of storage compartments that stores data cartridges for presentment to a robotic arm, which robotic arm includes a docking apparatus that mates with a corresponding feature on the array of storage compartments to ensure accurate alignment of the cartridge retrieval mechanism with the data cartridge.
It is a problem in the field of robotic cartridge library systems to provide an inexpensive yet reliable robotic arm to transfer data cartridges between their storage compartments and the drives that are used to read, write, and erase data that is stored on the data storage medium contained therein. In particular, it is a problem to reduce the dependence in such systems on the tight mechanical tolerances and vision systems that are required to precisely position the hand mechanism, located at the distal end of the robotic arm, in relation to the data cartridge.
In operation, the robotic arm removes a data cartridge from a storage compartment and inserts the cartridge into an appropriate media drive where data is read to/from the data storage medium contained in the data cartridge. The robotic arm then removes the data cartridge from the media drive at the appropriate time, and returns the data cartridge to its assigned storage compartment. The storage compartment has exacting dimensions that correspond to the data cartridge because the data cartridge must be positioned in a precise manner if the robotic arm is to grasp the data cartridge without mishap. In addition, the alignment of the hand mechanism, located at the distal end of the robotic arm, in relation to the data cartridge when the data cartridge is located in either the assigned storage compartment or the media drive represents a critical factor for reliable operation of the cartridge library system. In particular, a misalignment between the robotic arm and the data cartridge can cause a transfer failure. A robotic arm attempting to insert a miscentered data cartridge into a media drive may catch an edge of the data cartridge on an edge of the media drive. The torsion encountered when the robotic arm attempts to push the data cartridge into the media drive can twist the data cartridge sideways or even cause the data cartridge to drop from the hand mechanism of the robotic arm.
Robotic cartridge library systems provide relatively low cost access to a large amount of information. An example of this type of system includes the 4400 ACS system, which is commercially available from Storage Technology Corporation of Louisville, Colo.
The 4400 ACS system uses two concentric cylinders of cartridge storage arrays to house a large number of data cartridges. The robotic apparatus used in this system consists of a robotic arm assembly that is implemented by six independently operable servo mechanisms, which include a theta arm rotatably mounted on a support column. The robotic apparatus also includes a Z mechanism attached to the end of the theta arm, remote from the support column. The Z mechanism has coupled thereto reach, wrist and finger assemblies which perform the retrieval of the data cartridge from the storage compartment. The theta arm rotates the Z mechanism to the proper position in front-of a selected column of storage compartments in the array. The Z mechanism provides a vertical range of motion for the, reach wrist and finger assemblies to access the various vertical levels of the array of storage compartments. The robotic apparatus also includes a vision system that is equipped with illumination apparatus to generate an image of the selected data cartridge and its associated storage compartment to aid in the fine positioning of the robotic hand. This is accomplished by aligning the robotic arm with a target formed on the selected storage compartment, thereby ensuring precise orientation of the robotic hand with respect to the data cartridge stored in the selected storage compartment.
This robotic apparatus is extremely precise in its ability to locate and retrieve data cartridges. However, the mechanism used is expensive to implement. The expense of such robotic apparatus can be justified when the number of data cartridges served by such apparatus is large, but becomes prohibitive when the size of the library system is on the order of tens or even hundreds of data cartridges. Therefore, two of the problems in implementing a small or medium size cartridge library system is to reduce the dependence of such a system on the tight tolerances required by existing robotic servo mechanisms and to eliminate the need for a vision system to ensure precise alignment of the robotic hand with respect to the data cartridge.
The robotic docking apparatus for a cartridge library system having a cartridge storage array overcomes these problems by providing a docking apparatus on the robotic arm that mates with corresponding features on the storage compartments and media drives. The docking apparatus enables the robotic cartridge retrieval mechanism to automatically and precisely align with the storage compartment that contains the selected data cartridge by using passive alignment mechanisms and without requiring the use of a vision system or expensive tight mechanical tolerances on the robotic arm.
The robotic docking apparatus is incorporated into the robotic arm in the form of a docking feature that protrudes from the front of the cartridge retrieval mechanism. The docking feature is of length sufficient to begin engagement of the mating docking receptacle formed in each of the storage compartments in the storage array prior to the remainder of the cartridge retrieval mechanism contacting the data cartridge stored therein. The docking feature is tapered in shape, being narrower in width at the distal end thereof, so that as the reach mechanism of the robotic arm extends the cartridge retrieval mechanism toward the storage compartment the taper of the docking feature forces the cartridge retrieval mechanism into alignment with the docking receptacle. Thus, the alignment precision is a function of extent of the reach stroke, since the further the reach mechanism extends the cartridge retrieval mechanism toward the storage compartment, the more precisely aligned is the cartridge retrieval mechanism with respect to the storage compartment. The precision required for the initial alignment of the cartridge retrieval mechanism with respect to the storage compartment is determined by the taper (lead-in) of the docking feature, with greater the taper, less critical the initial alignment required.
In addition, the docking apparatus can be implemented with a wide variety of cartridge retrieval mechanisms. The gripper mechanism of the 4400 ACS can be used or, alternatively, the simple hook mechanism disclosed in the above-noted U.S. patent application Ser. No. 08/751,183 can be used to retrieve the data cartridge. In the implementation disclosed below, the hooking mechanism is used to mate with a hooking notch formed in the housing of the data cartridge. This hooking feature provides a simple, yet positive engagement of the cartridge retrieval mechanism to the data cartridge, which enables the cartridge retrieval mechanism to withdraw the data cartridge from the storage compartment without the need to provide complex and costly gripper mechanisms. In particular, the hooking feature is part of a retractable arm which, when hooked to a data cartridge, serves to pull the data cartridge from its storage compartment and into the cartridge retrieval mechanism by sliding the data cartridge into a receptacle formed in the distal end of the cartridge retrieval mechanism. This configuration eliminates the need for complex hand mechanisms yet provides a positive engagement between the robotic arm and the data cartridge for data cartridge extraction and insertion functions.
This docking feature/receptacle apparatus is therefore completely passive and can provide precise alignment between the cartridge retrieval mechanism and the storage compartment. This docking apparatus is inexpensive and obviates the need for a vision system for robotic alignment purposes. In addition, the docking apparatus reduces the need for high mechanical tolerances in implementing the robotic and storage array mechanisms since the cartridge retrieval mechanism is self aligning via use of the docking feature.